With the continuous improvements of people's requirements on future communications, more attention is paid to the spectrum efficiency of the cell edge, and how to improve the transmission quality and throughput of the cell edge become a research topic. The CoMP technique uses antennas of multiple APs for collaboration of transmission and reception, and one or more APs are set under one base station (cell). The coordinated multiple points in the CoMP may be multiple APs from one cell, or multiple APs from multiple cells, wherein, the cell includes a primary cell and coordinated cells of a terminal. The CoMP can effectively solve the problem of interference at the cell edge, so as to improve the capacity and reliability of the wireless link. Therefore, the CoMP technology, as a key technology, has been introduced into a Long Term Evolution-Advanced (LTE-A) system.
Under a Time Division duplex (TDD) mode of the CoMP system, a problem of antenna calibration between APs needs to be considered. After the antenna calibration is performed independently by the APs themselves, a reciprocity error may exist in an uplink-downlink radio frequency channel of the antenna of the AP, i.e., HDL=C*HUL, wherein, HDL and HUL are frequency-domain responses of a downlink channel and an uplink channel of the antenna of the AP respectively, and C is a complex scalar of an uplink-downlink channel reciprocity error. When Joint Transmission is performed on data between multiple coordinated APs, due to uplink-downlink channel reciprocity errors C of different APs are different, it will cause a phase difference and/or amplitude difference in the data transmitted by the coordinated APs, influence coherent transmission between the coordinated APs, and also influence the system performance. In order to reduce the phase difference and/or amplitude difference in the data transmitted by the coordinated APs, those skilled in the art propose a solution of calibrating transmission of data transmitted by coordinated APs in conjunction using an uplink-downlink channel response difference between the coordinated APs, but has not proposed a method for effectively calculating the uplink-downlink channel response difference between the coordinated APs.